temperature and heat temperature and thermometers is it hot or cold? mercury vs. alcohol...
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Temperature and HeatTemperature and Heat Temperature and Thermometers
Is it hot or cold?
Mercury vs. alcohol• Expansion or contraction of a material
Electrical resistance and infrared radiation
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Temperature and HeatTemperature and Heat Temperature scales
Reference points for setting the scale
• Why use water?
Triple point of water
• Solid, liquid and vapor all exist at the same time04/21/2304/21/23 APHY101APHY101 22
Temperature and HeatTemperature and Heat Absolute zero
Lowest temperature theoretically possible
• Lowest achieved is ~ 1x10-9 K• Average in space ~ 3 K
The KE is removed but not the quantum energy inside the atom – the electrons don’t stop moving
Is there a maximum temperature?04/21/2304/21/23 APHY101APHY101 33
Temperature and HeatTemperature and Heat Heat
Transfer of thermal energy between objects of different temperatures.
• Symbol: Q Unit: joules ( J )
High temperature does not always mean high thermal energy
Other units: BTU, calorie, Calorie (food)
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Temperature and HeatTemperature and Heat Internal energy
Sum of KE (linear, rotational, vibrational) and PE (chemical bonds within and between molecules)
• Model
The thermal energy of the system
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Temperature and HeatTemperature and Heat Thermal expansion
Most substances expand as their temperature increases and contract when cooled
Each material has a different expansion rate
Examples: Pyrex glass, dental fillings, bridges, concrete
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Temperature and HeatTemperature and Heat Thermal expansion of water
Water expands as it cools from 4°C to 0°C
• Effect on ponds, lakes and roads during winter
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Temperature and HeatTemperature and Heat Specific heat
A constant that relates heat per unit mass and temperature change in a material
• Metals have low values and water has a high value
Thermal inertia• Climate: land vs. oceans• Pizza: crust vs. sauce
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Temperature and HeatTemperature and Heat Conduction
Energy transfer due to particle contact• Atoms, molecules and electrons (metals)
Insulators and conductors• Building materials• Layers of clothing
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Temperature and HeatTemperature and Heat Convection
Energy transfer due to the motion of a fluid
• Currents are formed
Hot fluids rise and cold fluids sink• Cooling occurs when a fluid expands• Weather and climate
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Temperature and HeatTemperature and Heat Radiation
Energy carried by electromagnetic waves
• They can travel through empty space (vacuum)
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Temperature and HeatTemperature and Heat Radiation
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UVIRRadio
Temperature and HeatTemperature and Heat Radiation
All objects are emitters and absorbers of radiation
The rate of emission/absorption depends on the difference in T of the objects
Global warming• The greenhouse effect
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